The general responsiveness of Outlook 2007 has been increased by reducing the I/O disk usage processes and UI response times. Startup has been improved by moving long operations from the initial startup while shutdown time was decreased by making Outlook exit predictable. Finally the folder and view switching benefits from improved view rendering and folder switching routines.

The update is currently classified as a hotfix meaning that users will have to request it by providing their email address on a form at the Microsoft website. Users who do use Microsoft Outlook 2007 as their main email client will benefit from the update to a large extent. Startup time might be slower during first startup because of a one-time data structure upgrade.

Microsoft has updated their Mailbox Storage Size Guidance to reflect the performance and responsiveness improvements when utilizing Cached Exchange Mode with respect to mailbox/OST sizes:

• Up to 5 gigabytes (GB): This size should provide a good user experience on most hardware.
• Between 5 GB and 10 GB: This size is typically hardware dependent. Therefore, if you have a fast hard disk and much RAM, your experience will be better. However, slower hard drives, such as drives that are typically found on portable computers or early generation solid state drives (SSDs), experience some application pauses when the drives respond.
• More than 10 GB: This size is where short pauses begin to occur on most hardware.
• Very large, such as 25 GB or larger: This size increases the frequency of the short pauses, especially while you are downloading new e-mail. Alternatively, you can use Send/Receive groups to manually sync your mail.

The service pack for Outlook 2007 contains additional improvements for components like the Calendar or Outlook search among others. Interested users can read up on the Outlook 2007 SP1 update by visiting the extensive Microsoft Knowledgebase article and an official blog post covering the release announcement.